A Fast Lane Through the Stomach
2-D computer simulation reveals unexpected pathway
What goes into the stomach must come out, but perhaps not in the same order in which it entered, as gastroenterologists have long assumed. A two-dimensional computer model of human stomach digestion reveals a previously unknown narrow pathway that can funnel liquids from the top of the stomach to the intestines within 10 minutes.
“There are very few times you discover something that you weren’t expecting to find when you designed the experiment,” says James G. Brasseur, PhD, professor of mechanical engineering, bioengineering and mathematics at Penn State University and one of the researchers who created the model for studying drug delivery. But this was one such time.
The curious finding could help explain the wide variability in drug activation time: A drug might get swept along in this fast digestive current one time, and not another. The work appeared online in the Journal of Biomechanics in August 2006.
In 2004, Brasseur and research associate Anupam Pal, PhD, had published a computer simulation of gastric flow and mixing. In the current work, they used the same basic simulation, but studied gastric emptying. They gave unique numbers to thousands of points (fluid particles) uniformly distributed around the stomach. They then watched the order in which these particles left the stomach during a 10 minute simulation, while keeping track of each particle’s position at each time-step. When they then ran the simulation in reverse, they could watch the particles’ changing positions. After color-coding the points by time of leaving, they observed a ribbon-like path of gastric emptying that originates in the top of the stomach and passes along its side of least curvature. The entire animated sequence can be seen at http://mne.psu.edu/Brasseurlab/gastric/.
The researchers dubbed their discovery the “Magenstrasse,” which means “stomach road” in German. It is a sort of passing lane, where digested matter reaches the intestines more quickly than food and liquids outside the road. “We do not know if the Magenstrasse has a physiological function or if it is only a byproduct of the contraction waves in the distant stomach,” says Brasseur. The team showed that when the simulation excluded contractions known to exist at the bottom of the stomach, the Magenstrasse didn’t form.
“Brasseur’s modeling has revealed a potential new mechanism of liquid emptying that can explain why some patients take a very short time to absorb drugs in their bloodstream,” says Michael Fried, MD, director of the division of gastroenterology and hepatology at the University Hospital Zurich, Switzerland. He says pharmaceutical companies who wish to achieve constant and reproducible patterns of absorption of drugs must take this study into account. However, Fried notes, the model “has to be validated in animals or in humans.”
Brasseur agrees more research is necessary. “We would need further studies that checked how the path works with nutrients and drugs of different densities,” he says. He believes the Magenstrasse would still exist if the stomach contents are thicker than the viscous liquid used in his team’s simulations, but it may assume a different shape.